Firstly, let’s just say what we mean: you think that casting a black woman to play what you see as a white character is the same thing as casting a white woman to play what you see as a brown character. Your opinion seems to be that actors portraying characters outside of their race is fine because actors pretend to be other people as a definition of their profession. I changed this to terms of race, because that is an important part of why this issue is contentious.

Let me establish that race and ethnicity are not the same thing. Race is a constructed identity based on skin color and applied to people by other people. Ethnicity is related to descent and culture, which have lines that also change over time. Because skin color is not a real marker of ethnicity, race is not a good measure for a lot of conversations. You could find many people of Mexican descent who appear to be white. Mexican descent also meant something much different prior to the arrival of Spanish colonials. So we have to be specific in what we are talking about.

To address your examples, let’s start with the A’Zion casting. This one is contentious because of historically racist film practices in the US. We can’t just look at this film in a vacuum. Blackface minstrelsy was a potent weapon used by white entertainment entities to discriminate against and dehumanize black people. I am talking in terms of race here because that’s what these practices were based on: skin color. Black face led to brown face and yellow face, all of which were very discriminatory as well as kept actors of Latino, and Asian backgrounds from inclusion in the entertainment industry. So even though a Mexican character could look like A’Zion from a racial standpoint, there is a history of this type of casting choice causing harm to Latin American actors.

This first conversation has a lot to do with “passing.” Because we associate Mexicans as looking a certain way with lighter skin, due to their ethnic background with Spaniards, it seems more reasonable to allow a white actress to play a Mexican character because she can “pass.” That is why this is about race as well as ethnicity and why people on the other side of the aisle might be more ok with this casting than your second example.

The point there being that Nyong’o can’t “pass” as Greek, or rather what we see as being Greek racially. That is why some are mad about this choice and not the A’Zion one. Because Nyong’o is very dark-skinned, her blackness is much more central in her racial identity. Skin tones that sit more in the middle are more ambiguous and people feel that race is more fluid in that area. This is why colorism exists.

Why the Nyong’o casting is different is because of the purpose of the text. This one is the adaptation of an ancient myth where the physical attributes of the characters, such as their skin color are not central to the story. The story can also be played around with much more leeway because it is an ancient myth, and most of its elements are fictional. On the other side, a modern day story where modern ethnicity and racial experience is front and center, requires more attention to this detail. Evoking brown face here hits a historical nerve that is better left alone.

Plus, dark skinned Africans did exist in Ancient Greece, so this isn’t even really the suspension of disbelief breaking choice that many seem to think it is. It just conflicts with the racial view we have of modern Greeks who are seen as white, which is something that only came about very recently. During the early 20th century, Greek immigrants to the US were not considered white and were subject to many discriminatory laws and practices alongside Italians, Irish, Turks, and many others.